Research On The APSK Modulation And Demodulation Methods

Due to the increasing expense for channel estimation caused by the increment of the transmit and receive antennas in multiple-input multiple-output(MIMO)systems,channel estimation will certainly become an extremely challenging task for system designers in the incoming era for large scale MIMO.Especially in some cases of high-speed mobile communications,the huge expense for pilots and reference signals designed for real-time channel estimation under fast-fading channels will significantly decrease the system's spectral efficiency.Moreover,imperfect channel estimation will lead to considerable performance loss of the communication system.Since the non-coherent detection methods based on differential amplitude phase shift keying modulation can be conducted dispensing with channel state information,the channel estimation problem can be circumvented.However,most existing non-coherent detection methods are designed with the assumption that the system is equipped with only one transmit and receive antenna.As the detection complexity increases exponentially with the dimensions of the signal space,some non-coherent detection methods cannot be directly extended to MIMO systems.To solve this problem,this paper makes deep research on the APSK constellation design and MIMO modulation and demodulation methods.Besides,a novel non-coherent modulation and demodulation scheme combining APSK modulation and multiple symbol differential sphere decoding(MSDSD)is proposed.First of all,this paper improves the existing MSDSD technology from three different aspects: the vast number of matrix inversion operations in existing MSDSD algorithms are avoided by conducting matrix triangular decomposition and deducing a recurrence formula;taking advantages of the characteristics of APSK constellations,i.e.,the constellation points are distributed on multiple concentric rings,the complexity of the algorithm is reduced;the MSDSD complexity is further reduced by overlapping successive detection windows.Theoretic and simulation results indicate that the improved algorithm is able to reduce the MSDSD complexity by an order of magnitude compared with existing methods,and in the mean time maintain the same system performance.Then,the improved non-coherent detection method is extended so that it can be applied in MIMO systems.Firstly,based on the concept of spatial modulation,a novel absolute amplitude differential phase transmission scheme is proposed.This scheme can not only enhance the system throughput,but also improve the degree of freedom in terms of APSK constellation design,and avoid inter-channel interference.Based on that,this paper extends the improved MSDSD so that it can be applied in the proposed transmission scheme.Besides,APSK constellation designs,which include 16 APSK,32APSK,64 APSK,and 128 APSK constellation and bit mapping designs,are conducted to achieve higher power efficiency.The simulation analysis at the end of this paper indicate that system designers can achieve a good compromise among system throughput,detection complexity,and system performance by adjusting the number of transmit and receive antennas,the order of APSK constellations and the number of overlapped symbols between successive detection windows.